SERS nanotags have proved useful for marking objects for identification and tracking. SERS nanotags are nanoparticulate optical detection tags which function through surface enhanced Raman scattering (SERS). SERS is a laser-based optical spectroscopy that, for molecules or other materials, generates a fingerprint-like vibrational spectrum with features that are much narrower than typical fluorescence.
Typically, a SERS active molecule associated with a tag is excited by laser light at a specific excitation wavelength. Many SERS active molecules can be excited at several alternative wavelengths with each wavelength causing the emission of a characteristic SERS spectrum. In some marking uses the ability of a known SERS nanotag to be interrogated at multiple suitable interrogation wavelengths is an advantage. In other implementations, such as covert item marking, the ability to excite a SERS nanotag at multiple wavelengths is potentially a disadvantage, since this makes covert tags easier to detect by third parties. It is difficult however to manufacture a SERS nanotag that can be interrogated at a limited number of otherwise suitable wavelengths with conventional SERS reporter molecules.
The embodiments disclosed herein are directed toward overcoming these or other problems associated with known surface enhanced spectroscopy particles.